Abstract The focus of this proposal is the development of novel chimeric antigen receptor (CAR) T cells that specifically target and eliminate CD4+ autoimmune T cells, and will therapeutically alter the disease course of autoimmune arthritis. This innovative approach is based on the generation of CD8+ T cells genetically engineered to express HLA-DR CAR molecules loaded with an autoantigenic peptide. Using our well characterized HLA-DR humanized mouse model of rheumatoid arthritis (RA), we will test the hypothesis that CD8+ T cells can be engineered to express HLA-DR class II CAR with CD28/CD3? intracellular signaling domains, and that after peptide loading of the CAR DR molecules on these CD8+ T cells, they will function as CTL and specifically target and eliminate CD4+ autoimmune T cells. Two approaches will be pursued to generate antigen specific targeting of the CD4+ T cells. Initial experiments will be focused on using DRB1 cDNA encoding an antigenic peptide that is covalently linked to the DR1 molecule. This approach will be used to demonstrate the feasibility of the CAR CTL generation and their function in vivo in the inhibition of an active autoimmune disease. In the second approach, we will generate CAR CTL with ?empty ? DR1 molecules, and soluble peptide will be used to load the DR1 CAR before measuring the CAR CTL function. This approach will allow for targeting CD4+ T cells specific for posttranslationally modified (PTM) peptides which are components of the autoimmunity of the mouse model and potentially important components of RA autoimmunity. Through the specific aims of this proposal, we will investigate the specificity of the CAR T cells, their ability to receive signals through the CAR CD28/CD3 domains, and their efficacy in treating an active autoimmune disease.